2 functions, and use them to disable interrupts for polled commands.
In siisata_probe_drive(), disable interrupt while resetting the PHY and
sending the SOFT_RESET FIS. Also dectect timeout/errors at this level and
disable the port if needed.
Make siisata_intr_port() more resistent to interrupts without xfer (especially
error interrupts which can be asynchrounous, but can also happen for
timed out xfer).
With this, the kernel doesn't pannic when a siisata controller is connected
to a SATA port multiplier. More work is needed to support port multiplier
though.